Given a convex function \(f:(0,\infty )\rightarrow \mathbb {R}\)  such that \(f(1)=0\) , the \(f\) -divergence between two probability measures \(P\ll Q\)  is defined as [1]}, [2]}
\(D_f(P\Vert Q){\mathbb {E}}_Q\Big [f\big (\frac{\textnormal {d}P}{\textnormal {d}Q}\big )\Big ].\) 
